1. Field of the Invention
The present invention relates to a backprinting recording medium.
2. Description of the Related Art
Backprinting recording media are known as a class of recording media used in ink-jet recording systems. Typical backprinting recording media are configured such that an ink-absorbing layer composed of a resin material capable of absorbing and fixing an ink-jet recording ink is formed on a transparent substrate such as a polyester sheet, and a porous ink-permeable layer produced by dispersing a filler in a binder resin (Japanese Patent Application Laid-open No. 10-211763, Japanese Patent Publication No. 6-71822) is formed on the ink-absorbing layer. When ink-jet recording is performed on such backprinting recording media, the ink jetted on the ink-permeable layer penetrates from the surface of the ink-permeable layer through the layer, and reaches the ink-absorbing layer, where the ink is absorbed and fixed by the ink-absorbing layer. Ink images are thus formed in the ink-absorbing layer. The ink images thus formed are viewed through the transparent substrate.
The above-described backprinting recording media are disadvantageous, however, in that the ink-permeable layer has insufficient coating strength. The result is that when recording is performed on a backprinting recording medium in an ink-jet printer, the porous structure of the ink-permeable layer is damaged in the areas where the medium is pressed down with the feed rollers of the printer, ink permeability decreases in these areas, and the quality of the ink images is deteriorated. When the ink images are viewed in transmitted light, there is a difference in light transmittance between areas of reduced ink permeability (compressed areas) and areas of normal ink permeability (uncompressed areas), and the ink images acquire visible feed roller marks.
It has been suggested that this shortcoming can be overcome by increasing the content of binder resin in the ink-permeable layer and enhancing the coating strength of this layer, but this approach has the unwanted effect of reducing the ink permeability of the ink-permeable layer and preventing the ink-absorbing layer from absorbing the amount of ink necessary to form high-quality images.
An object of the present invention is to provide high-quality ink images while an ink-permeable layer is prevented from losing some of its ink permeability when a backprinting recording medium is pressed down with the feed rollers of a printer, and no feed roller marks can be seen when the ink image is viewed in transmitted light.
The inventors perfected the present invention upon discovering that the ink permeability and coating strength of the ink-permeable layer of a backprinting recording medium is closely associated with the Shore D hardness and glass transition temperature of the binder resin used.
Specifically, the present invention provides a backprinting recording medium, comprising a transparent substrate, an ink-absorbing layer formed on the transparent substrate and a porous ink-permeable layer formed on the ink-absorbing layer and produced by dispersing a filler in a binder resin, wherein the binder resin constituting the ink-permeable layer has a glass transition temperature of 10xc2x0 C. or higher, and a Shore D hardness at 25xc2x0 C. of 40 or higher. As referred to herein, the glass transition temperature of the binder resin may preferably be 130xc2x0 C. or lower, and the Shore D hardness (25xc2x0 C.) may preferably be 90 or lower.